The present invention relates generally to cryogenic integrated circuits, and more specifically the invention pertains to a packaging apparatus that is used to expose semiconductor devices and other objects to a coolant without contaminating the semiconductor devices.
In the past, cryogenic circuitry has been operated in a bath of liquid, for example liquid nitrogen at its boiling point, in order to obtain the advantages of superior removal of generated heat that evaporative cooling can provide. Such operation has always been done either with the semiconductors exposed to the liquid directly or with the semiconductors in hermetically sealed packages. The former has the problem that, when the system is removed from the bath, the semiconductors are exposed to atmosphere and its contaminants unless elaborate precautions are taken. The latter arrangement prevents exposure to the atmosphere but isolates the semiconductors from direct contact with the liquid. That reduces the effectiveness of the cooling.
The task of providing a packaging method is described which permits the exposure of semiconductor devices to a coolant without risking contamination during acquisition, installation or removal, is alleviated to some extent by the system disclosed on the following U.S. Pat. Nos., the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 5,040,053 issued to Porter et al; PA1 U.S. Pat. No. 4,805,420 issued to Porter et al; PA1 U.S. Pat. No. 4,758,926 issued to Herrell et al; and PA1 U.S. Pat. No. 4,734,820 issued to Lauffer et al. PA1 1) substantially above the boiling point of the coolant substance and; PA1 2) substantially below the minimum temperature to which the enclosure is to be subjected while remaining sealed in the presence of a specified external pressure and; PA1 3) such that sufficient coolant substance will be trapped within the apparatus to create a second specified pressure within the apparatus of a specified maximum temperature. PA1 1) substantially below the minimum temperature to which the enclosure is to be subjected while remaining sealed in the presence of a second specified external pressure and; PA1 2) above the condensation temperature of the coolant substance at the second specified external pressure.
The patents identified above relate to systems for cooling electronic components. In particular, the Porter et al '053 patent describes a cryogenically cooled integrated circuit apparatus which comprises a vessel for holding cryogenic fluid and an integrated circuit package positioned within an opening at one end of the vessel. The circuit package includes a circuit die, a protective body with first and second faces, a metal lid, and a plurality of metal pins. The protective body surrounds an edge portion of the die. The metal lid is attached to the die and to a portion of the first face of the protective body. The package is positioned so that the lid is in direct contact with the fluid and the pins extend away from the vessel.
The Porter et al '420 patent relates to a cryogenic vessel for cooling electronic components. The vessel is divided into two portions with each portion having an outer wall and an interior immersion chamber. A membrane located between the vessel portions and separating the two chambers contains openings for fluid transfer between the two chambers and an exterior point. Sealing members located between the membrane and each of the vessel portions provide a fluid tight seal of the immersion chambers. An electronic component mounting socket is located on a portion of the membrane within the immersion chambers for mounting an electronic component to be cooled. Cryogenic fluid is introduced into the immersion chambers through a supply conduit in the outer wall of one of the vessel portions.
The Herrell et al patent describes a package for enclosing and cooling semiconductor integrated circuit chips. The package includes a generally planar substrate on which the chips are positioned. A heat sink is positioned in contact with the chips and includes microchannels through which a cooling fluid flows to transfer heat generated by the chips.
The Lauffer et al patent is directed to a cryogenic packaging system for removable mounting an integrated circuit package having a plurality of electrical pins. A plurality of mating pins is provided where each pin has a receptacle filled with liquid mercury, and is connected to an electrical pin of the integrated circuit package. Reducing the temperature causes the liquid mercury to solidify and firmly bonds the electrical pins together. The entire assembly is inserted into a Dewar type vessel and covered with a low temperature liquified gas to cool the integrated circuit package. Although these patents relate to systems for cooling electronic components, they do not describe a system where the enclosure containing the components is evacuated at room temperature, cooled in an atmosphere of clean coolant gas, and then heated to evaporate the resulting liquid and trap cold gas inside the enclosure.